ITU recommendation G992.1 specifies how the maximum bandwidth which can be supported over a particular ADSL connection between a particular Remote ADSL Transceiver Unit (ATU-R) and a particular Central office or network operator ADSL Transceiver Unit (ATU-C) may be determined at the time of initiation of the ADSL connection (see G992.1 Chapter 10) and may even be periodically re-negotiated during a connection (see G992.1 Appendix II); the maximum bandwidth in fact depends upon various factors which will differ from line to line and from time to time depending on things such as the amount of electromagnetic noise present in the environment of the ATU-R, etc.
However, despite this, it is common in most practical implementations of ADSL for a network operator to offer an end user a fixed bandwidth (commonly offered values being 500 kb (kilo bits/second), 1 Mb (Mega bits/second) and 2 Mb). In such circumstances, the initiation process happens in the standard way to establish the maximum bandwidth available over the connection, but instead of then setting up the connection at that maximum setting, it is simply checked whether or not this maximum is at least equal to the contractually agreed bandwidth, and if so, then the connection is made at this agreed amount (rather than the maximum available) but otherwise the connection is just not made at all.
Because an access network is likely to contain a large number of DSLAMs they have generally been designed to operate as autonomously as possible. As such, although they will generally store some useful data about each digital subscriber line (hereinafter referred to simply as a “line”) to which it is connected such as the theoretical maximum rate at which the line could have been connected last time an ADSL connection was set up over the line, each DSLAM operates according to a server client model where each DSLAM operates as a server and only reacts to requests issued to it from a client. Thus in current DSLAMs, in order to access information about an individual line a requesting device generally needs to issue a request to the DSLAM and await a response.